This invention relates to a bootlace-type lens used to feed a planar radiating antenna array and more particularly to a small-size, three-dimensional bootlace lens having very little, if any, aberrations.
Prior-art antennas have been made in various shapes, sizes and for different frequencies of operation. Various types of lens have been used to feed the various types of antennas and to receive signals from an antenna due to incident radiation.
The bootlace lens was developed by H. Gent in 1956 as set forth in the following: (1) "The Bootlace Aerial", Royal Radar Establishment J., pp. 47-57, Oct. 1957; and (2) British Pat. No. 25,926/56 Aug. 1956 by Gent et al. Such a lens uses a planar homogeneous wave-transmission region which has a set of feed ports on one side and a set of lens ports on the other. For the case in which the radiator array is constrained to a straight line, it has been shown that perfect focus can be obtained at three points on the feed curve, as set forth in an article, "Two-dimensional Symmetric Bootlace Lenses", IEEE Trans. Antennas Propagation, Vol. Ap 13, pp. 521-528, July 1965.
Design equations of the bootlace lens were presented by Rotman and Turner, in 1963, and they also gave examples of aberration characteristics in an article, "Wide-angle microwave lens for line source Applications", IEEE Trans. Antennas Propagation, Vo. AP-11, No. 6, pp. 623-632, Nov. 1963. Archer has described applications of the lens in an article, "Lens-fed Multiple-beam Arrays", Microwave, Vol. 18, No. 10, pp. 37-42, Oct. 1975. Whereas the primary intended application of the lens in the 1950's was for rapid mechanical scan by means of feed motion, recent interest has been based on the lens' capabilities as a multiple-beam system. Gent lenses have been used recently in experimental precision aircraft landing systems in Australia and the United States which has been set forth in an article, "MLS-A Practical Application of Microwave Technology", IEEE Trans. Microwave Theory Tech., Vol. MTT-24, No. 12, pp. 964-971, Dec. 1976.
Rotman and Turner required that the feed curve be circular, and optimized the design parameters accordingly. This was consistent with rapid mechanical scan of the feedhorn. In terms of multiple-beam configurations, requiring the feed curve to be a circle is an unnecessary constraint. It has been concluded that there is no limitation on the shape of the feed curve; however, the lens should exhibit front-to-back symmetry.
An unusual two-dimensional bootlace lens has been set forth in U.S. Pat. No. 4,114,162.